This is a multivariate young adult follow-up of a core sample of 108 boys with the Hyperkinetic/Minimal Brain Dysfunction (HK/MBD) Syndrome and 52 of their full brothers, plus a replication sample of 52 boys with the HK/MBD Syndrome and 25 of their full brothers. The core and replication patient samples were originally seen as outpatient referrals to the University of Iowa Child Psychiatry Service between 1967 and 1972. The core sample was followed up five years after referral as young adolescents. Data from referral and adolescent follow-up are now stored on tape as easily accessible computer archives. In the proposed young adult follow-up, all subjects are to be seen within one year after their 21st birthday and administered a multi-trait and multi-method battery of cognitive, achievement, personality, and psychiatric tests, interviews, and ratings. Results of planned multivariate analyses will provide a replicated description of HK/MBD boys as young adults, with sibling controls. Data will also be available to identify, by means of multiple regression, potential background, symptom, and treatment predictors of adult status. Taken together, we believe these samples will comprise the largest and most comprehensive longitudinal data resource of its kind, offering unique opportunities for generating and refining hypotheses about this most prevalent of childhood disorders.